1. Field of the Invention
This invention relates to bearings having a lining of babbitt material. More particularly, this invention relates to a method of lining a bearing shell with babbitt material.
2. Description of the Prior Art
Prior art methods of manufacturing babbitt lined bearings generally call for a cylindrical bearing shell made of steel having an inner cylindrical surface to which a babbitt lining is applied. The cylindrical surface is cleaned with an acid and the clean shell is heated. Once heated, the surface is tinned, for example, by emersing the shell in a tin bath or by spraying tin onto the surface. Once tinned, the bearing shell is rotated about a horizontal axis coaxial with the cylindrical axis of the bearing shell. While the shell is rotating, a molten babbitt metal is poured onto the surface and allowed to cool as the shell rotates. The babbitt solidifies and forms a bond with the layer of tin which in turn is bonded to the steel surface. Rotation is stopped and the babbitt is machined to a final desired thickness.
The above-described method of lining a bearing shell with babbitt metal presents several problems. First, the acid cleaning and tinning procedures are difficult to accomplish properly. For example, a small area of the shell surface may not be adequately cleaned or tinned. In such cases, the babbitt metal does not properly bond to the shell resulting in failure of the bearing at low loadings. Additionally, the cleaning and tinning require several heating steps and frequent handling of the piece. Also, the process requires a good deal of babbitt material to provide enough material for final machining. Commonly, three-quarters of an inch to one inch minium thickness is required following solidification to insure sufficient thickness in valleys formed in the babbitt during cooling.
One method of improving the bond between the babbitt and the shell is to machine a series of dovetailed grooves in the shell which receive the molten babbitt and provide a mechanical bond in addition to the metallurgical bond. However, this method requires costly machining. A method for improving the metallurgical bond between the babbitt and the bearing shell is taught in U.S. Pat. No. 4,117,580 to Heck dated Oct. 3, 1978. The method as taught by Heck consists of lining the bearing surface of the shell with a slurry of tin powder, water and a flux and heating the shell to a temperature sufficient to tin the bearing shell and convert the water to steam. A mixture of water and flux is applied to the layer of the tin on the babbitt shell while the bearing is hot and molten babbitt is poured onto the bearing shell as the shell is rotated about a horizontal axis. The water containing vapor surrounding the shell provides an atmosphere which reduces oxides, such as tin oxides, formed during application of the tin layer. The flux is carried away from the tin during rotation of the bearing shell.
Notwithstanding the improvements made in the prior art, the process for making babbitt lined bearings is still exceedingly expensive in both time and materials. Specifically, the tinning process is expensive and time consuming and carries an inherent possibility of a poorly tinned surface resulting in a poor babbitt bond. Also, the casting of molten babbitt is not easily controlled for desired thicknesses which results in a large amount of finished machining which is required to bring the babbitt lining to its designed thickness. Also, tin oxides which are not fully reduced can cause a poor metallurgical bond between the babbitt and the bearing shell.